The present invention relates to a fastener which is pressable into a metal sheet in a way safe against rotation and pressing out, having a head or ring the side of which after insertion facing the metal sheet has radially positioned ridges, which, when setting the fastener, are pressed into the metal sheet, wherein a cylindrical thread-carrier is positioned in the center of said ridges projecting through the metal sheet beyond the other side of the metal sheet and which in the vicinity of the side of the head or ring facing the metal sheet in the set state has an annual recess into which the material of the metal sheet displaced during the setting can be pressed.
Such fasteners can be performed as bolts (having a shaft with an exterior thread) as well as nuts (having a through bore with an interior thread). A corresponding fastener for example is known from WO 94/01688.
Similar constructions for example are known from DE 44 10 475 A1, DE 195 35 537 A1 and WO 98/51934.
In all these known fasteners, the problem exists that these cannot be used with a metal sheet whose thickness is 1 mm or less or can be used only with a decreased function since the corresponding safety against rotation and pressing out is no longer obtained.
Accordingly, it is the task to be solved by the present invention to improve such a fastener in such a way that the fastener can be used with metal sheets having a thickness of an even below 1 mm and still achieve sufficient safety against rotation and pressing out without the necessity of a special preparation of the opening into which the fastener should be set. In solutions as e.g. according to DE 44 10 475 A1 or WO 94/01688 around the opening for setting a so-called xe2x80x9ccollarxe2x80x9d of metal sheet has to be formed to achieve a sufficient safety against rotation and pressing out with thinner metal sheets. This necessitates in a disadvantageous way a further procedural step to form the corresponding xe2x80x9ccollarsxe2x80x9d.
According to the state of art until now one has assumed that an optimal safety of the fastener against rotation and pressing out is achieved if in the vicinity of the thread-carrier as much space as possible is provided to receive the metal sheet material. With thinner metal sheets however not sufficient material of the metal sheet is present to fill such spaces. According to the prior art therefore auxiliary constructions have been used as for example the xe2x80x9ccollarxe2x80x9d from the WO 94/01688.
Contrary to the above, the present invention starts out from the fact that, for achieving an optimal safety against rotation and pressing out with thinner metal sheets, not too much space for the displaced material of the metal sheet should be provided but only that volume, which by a deliberate deformation (flowing) of the metal sheet, can be filled in an optimal way. This shaping into the annular recess is achieved by a flow shaping of the metal sheet material caused by the special shape of the ridges.
According to the invention, the above task is solved by the features that the ridges over a majority of their radial extension have a constant height and width and in the vicinity of the thread-carrier smoothly merging with the same with an increasing width.
By such a construction even with very thin metal sheets, a sufficient safety against rotation and pressing out of the fastener is achieved.
For a further improvement of the safety against rotation according to the invention it is preferred that the ridges have a basically rectangular cross-section and their side wall are perpendicular to the side of the head facing the metal sheet. By this, the grip of the ridge in the metal sheet material is further improved.
To achieve a close contact of the head on the metal sheet and thereby to avoid the formation of gaps it is useful if the ridges in the radial exterior area taper off in a flat manner.
For this purpose, it is of advantage, too, if the ridges in the radial exterior area taper off sidewardly in a rounded manner.